This invention relates to wide band gap semiconductor light emitting devices (LED's), and also relates to such devices including a Fabry-Perot cavity to achieve laser output.
Semiconductor LED's fabricated from wide band gap materials such as II-VI compounds, are desirable in that they emit radiation at wavelengths within the visible region of the electromagnetic spectrum. However, at the present time, it is difficult to make pn junction LED's from wide band gap semiconductor materials, since suitable materials can generally only be properly doped either with n-type or p-type conductivity.
Despite these drawbacks, lasing has nevertheless been achieved in devices utilizing wide band gap semiconductor materials of a single conductivity type, usually by avalanche breakdown brought on by a high field potential, for example in the vicinity of a boundary between regions of different conductivities. In this regard, see Fern et al., U.S. Pat. No. 3,493,891 (p-GaAs), and Mimura, Japanese patent application No. 54-14470 (n-GaAs). Lasing in such single conductivity type materials has also been achieved by a high field potential induced behind the ionization front of a streamer. See N. G. Basov et al., Semiconductor Streamer Lasers, J. Quantum Electronics, Vol. QE-13, No. 8, August 1988 (Cd.sub.x Se.sub.1-x and ZnSe). In addition, lasing has been reported by means of direct carrier injection from a Schottky diode. See Wade, U.S. Pat. No. 3,382,454 (p-GaAs). Lasing is also generally known to be achieveable in such materials by pumping optically or with a high energy electron beam.
Electron beam excitation of II-VI materials is of particular interest for display applications, such as video, since the technology for scanning a display screen with electron beams is well developed, and since the band gap energies of these materials are such that well defined emissions within the visible spectrum are obtainable. However, the efficiencies of LED's using such single conductivity type materials are less than could be obtained if such materials could be doped both n- and p-type, to obtain pn junctions. For such single conductivity-type materials, the electron beam energies required to achieve carrier multiplication by avalanche breakdown, the most efficient mode of operation, would be practically prohibitive.
Accordingly, it is an object of the invention to provide wide band gap, single conductivity type, semiconductor LED's which can be excited by electron beams at energies below those previously required.
It is another object of the invention to provide wide band gap, single conductivity type, semiconductor lasers which can be excited by electron beams at energies lower than those previously required.
It is still another object of the invention to provide wide band gap, single conductivity type, semiconductor LED's and lasers having enhanced efficiencies of operation.
It is still another object of the invention to provide wide band gap, single conductivity type, semiconductor heterostructure LED's and lasers having enhanced efficiencies of operation.